An analysis of the 2000 census suggests that some Asian-American parents of girls may be using advances in prenatal technology to ensure they get a boy the next time around.

MICHELE NORRIS, host:

The preference for sons, particularly first-born sons, has long been deeply rooted in some Asian societies. A new study using census data finds that a growing number of Asian-American families may be asserting that same preference here in the U.S., and they're doing it with the help of medical technology.

The findings focus on children born in the U.S. to Chinese, Korean, and Asian Indian parents. The findings appear in today's edition of Proceedings of the National Academy of Sciences. The study was co-authored by Douglas Almond and Lena Edlund, a team from Columbia University.

And Dr. Almond joins us now from New York.

Welcome to the program, doctor.

Dr. DOUGLAS ALMOND (Economist, Columbia University): Thank you very much for having me.

NORRIS: Now, using the census data, could you briefly describe what you set out to find in the study?

Dr. ALMOND: Sure. What we set out to find was basically, do we observe in the United States the same thing that we observe in certain Asian countries? And that is, following the birth of a daughter, are subsequent children more likely to be sons than is the biological norm, which is about 1.05 or 1.06 sons per one daughter.

NORRIS: And what did you find?

Dr. ALMOND: When there's a third child following two daughters, it's 50 percent more likely that a son is born if the parents are Chinese, Korean or Asian Indian. And we see no difference for whites if the first two children were girls.

NORRIS: Fifty percent more likely. That's a much higher ratio than you would normally see.

Dr. ALMOND: That's right. The ratio is usually about 5 percent more likely to have a son.

NORRIS: What does this suggest? Why is this happening?

Dr. ALMOND: I think we should say we don't really know. We're documenting this empirical finding. To us, given the context that in certain Asian countries there's a traditional preference for sons, that desire of sons is being exercised not only in Asia but in the United States, and that the technologies for prenatal sex determination, there's now evidence that those are being used to generate male birth.

NORRIS: It sounds like you're saying that these findings suggest that some Asian families are practicing a form of sex selection, gender selection.

Dr. ALMOND: Yes. That's what we think is going on. The results that we find in the census are confirmed when looking at linked natality data, so we can I think safely conclude that this is not something that's happening following birth. It's something that's happening prenatally or around conception. And speaking as an economist, I guess, the cheapest way to achieve that is through a prenatal ultrasound and sex-selective abortion.

NORRIS: Again, we should emphasize that you're not entirely sure why this is happening. But in terms of the medical technologies that families might be using, you mentioned ultrasound and then abortion. Are there other things that families would do before conception?

Dr. ALMOND: There are other technologies. There's in vitro technologies and there's sperm-sorting technologies that can be used, and those are substantially more expensive.

NORRIS: When these medical technologies first became available, whether you're talking about amniocentesis or ultrasound or in vitro fertilization, there was a debate that still continues today about this concern that parents might participate in gender selection. What are the implications, potential implications of this finding?

Dr. ALMOND: Right. Well, one implication is that we should have more of that debate again. There are countries that customarily do not reveal the sex of the baby with a customary prenatal ultrasound. Sweden is one such country.

NORRIS: Dr. Almond, were you surprised by these findings?

Dr. ALMOND: We really were. And the reason why we're so surprised is, though the high sex ratios following female births have been noted in certain Asian countries, it has not been noted in the United States. Furthermore, the explanations that are often given for the high sex ratios in Asian countries are things that do not exist in the United States, things like the one-child policy or widespread dowry payments in the case of India. So the expectation was, absent those things, we would observe similar sex ratios to the population norm.

NORRIS: Dr. Almond, thank you very much for speaking with us.

Dr. ALMOND: Thank you for having me.

NORRIS: Dr. Almond is the co-author of a study, along with his colleague Lena Edlund from Columbia University, of findings that are released today in the Proceedings of the National Academy of Sciences.

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